// CODE SNIPPET
701.10 Louvers, Grilles, and Screens
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The required size of
openings for combustion, ventilation, and dilution air shall
be based on the net free area of each opening. Where the free
area through a design of louver, grille, or screen is known, it
shall be used in calculating the size opening required to
provide the free area specified. Where the louver and grille
design and free area are not known, it shall be assumed that
wood louvers have 25 percent free area and metal louvers and
grilles have 75 percent free area. Nonmotorized louvers and
grilles shall be fixed in the open position. [NFPA 54:9.3.7.1]
Screens shall be
not less than 1/4 of an inch (6.4 mm) mesh. [NFPA
54:9.3.7.2]
Motorized louvers shall
be interlocked with the appliance so they are proven in
the full open position prior to main burner ignition and
during main burner operation. Means shall be provided to
prevent the main burner from igniting where the louver fail to open during burner start-up and to shut down the
main burner where the louvers close during burner operation.
[NFPA 54:9.3.7.3]
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